There are many different types of window shades on the market such as Venetian blinds, pleated window shades and the like. Some of them are installed by users after purchased. They have to measure first against the width of windows or doors to be installed, and the extra length of the shade has to be cut off if their width is greater than the width of the windows or doors.
U.S. Pat. No. 7,000,521 B1 discloses a pleated shade cut-off apparatus A as shown in FIG. 1. It mainly includes a screw bar A1 driving a blade A2 up and down so that the diagonal cutting edge A21 of the blade A2 can be moved up and down for a selected cutting distance. To accomplish cutting a huge force has to be applied on the screw bar A1. It takes a great effort and is not very practical. FIG. 2 illustrates another U.S. Pat. No. 6,435,066 B1 which is a cutting apparatus for window covering. The cutting apparatus 10 mainly includes an arm 11 pivotally coupled with a gear 12 to drive an engaged gear rack 13 so that a blade 14 also is driven to move a diagonal cutting edge 141 downwards to cut off a wound window shade. When in use a force is applied to the arm 11. To save cutting effort the arm 11 should be made at a greater length. As a result, a greater operation room is needed.